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Own Properties and Object.fromEntries

Object.hasOwn checks whether a property belongs directly to an object, independent of its prototype. Object.fromEntries builds an object from key-value pairs. These methods support record manipulation without confusing inherited methods with data; Object.hasOwn was added in ES2022.

Syntax

Object.hasOwn(record, "key");
Object.fromEntries([["key", "value"]]);

Examples

Own Properties and Object.fromEntries: working example

Run this standalone example in a modern browser console unless another environment is specified. Expected result: The console prints true false, then true 3.

const record = Object.create({ inherited: 1 });
record.count = 0;
console.log("inherited" in record, Object.hasOwn(record, "inherited"));
const prices = Object.fromEntries([["tea", 3], ["coffee", 4]]);
console.log(Object.hasOwn(record, "count"), prices.tea);
  1. Expected result: The console prints true false, then true 3.
  2. The in operator sees the prototype property; hasOwn does not.
  3. An own property can exist even when its value is falsy, so truthiness is not an existence check.

Best practices

  • Use Map when keys are not naturally object property names.
  • Remember that repeated keys in fromEntries overwrite earlier values.

Runtime & versions

Browsers and JavaScript runtimes. Feature availability depends on the language and runtime version used by your project; consult the official reference below.

ECMAScript specification

Specifications & further reading